Ceramic Biomaterials for Dental Implants: Current Use and Future Perspectives

Although titanium implants have the longest traceable record of predictable clinical performance and by far the widest diffusion in the market, some drawbacks have been recently pointed out. Titanium is not a completely bioinert material, since it may elicit allergenic reactions and is capable to diffuse not only within the adjacent tissues, which is proven by the elevated concentrations found in peri-implant bone and regional lymph nodes, but also systemically. Ceramic materials for oral application have been used for 40 years. Presently, the material of choice is yttria-stabilized tetragonal zirconia, which presents excellent mechanical and tribological properties together with biocompatibility. Concerns remain about the long-term durability of the material, owing to the report of in vivo failures that were caused by the low-temperature degradation of zirconia. To address this issue, research has developed improved oxide-based materials such as alumina-zirconia composites along with non-oxidic ceramics such as silicon nitride. The proposed book chapter deals with the above-mentioned improved ceramic materials, based on both scientific literature and the authors' direct experience. Particular emphasis is given to the major achievements attained so far in terms of the biological response supported by the interface. Original in vitro data regarding alumina-toughened zirconia (ATZ), zirconia-toughened alumina (ZTA), and silicon nitride (Si3N4) samples with different surface modifications are shown. Accurate surface characterization was achieved recurring to scanning electron microscopy, non-contact optical profilometry. Protein adsorption on the surface was determined. A mouse pre-osteoblastic cell line, that is MC3T3-E1, was used to examine cellular adhesion and morphology. Viability and proliferation rate of MC3T3-E1 cells were assessed with proper chemiluminescent kits. Cell differentiation was obtained in terms of calcium deposition within the extracellular matrix and quantification of keynote osteogenic markers. Data were analyzed by GraphPad Prism6. For the first time, the behavior of osteoblasts cultured on ATZ and ZTA that underwent a patented hydrothermal treatment was reported. Also, two different surfaces of Si3N4 were compared. MC3T3-E1 cells could properly spread in all the experimental conditions tested. The proliferation rate was consistent with that expected for biocompatible materials. Hydrothermally treated ATZ samples and Si3N4 rough surfaces were capable to enhance the osteogenesis in vitro. The biological responses induced in MC3T3 cells were correlated with the surface features. Immediately after seeded, osteoblasts are known to interact with their substrate via integrins that bind to the proteins adsorbed on the biomaterial surface. The interface effect was discussed in light of the literature. The most recent publications suggest that research aims at investigating the effects of surface modifications dictating the chemical characteristics and the nano-/micro-topography that are paramount modulators of the biological response.